1. Field of the Invention
The present invention relates to a valve timing adjuster that adjusts timing of opening and closing an intake valve or an exhaust valve of an engine.
2. Description of Related Art
A conventional valve timing adjuster includes a housing (first rotor), and a vane rotor (second rotor). The housing is rotatable synchronously with one of an engine output shaft and a camshaft that opens and closes an intake valve or an exhaust valve. The vane rotor is rotatable synchronously with the other one of the output shaft and the camshaft. Also, the housing has therein advance hydraulic chambers and retard hydraulic chambers defined by vanes of the vane rotor. Then, a phase control is performed to adjust a relative rotational position (relative rotational phase) of the vane rotor relative to the housing by adjusting pressure of hydraulic oil supplied to the advance and the retard hydraulic chambers in order to adjust timing of opening and closing the valve.
However, if a drive source of a hydraulic pump, which supplies hydraulic oil, serves as the engine output shaft, the hydraulic oil may not be substantially supplied immediately after the starting of the engine. Then, the relative rotational phase may be substantially varied due to the position change of the vane rotor that is subjected to variable torque (torque reversals) applied through the camshaft caused by a valve spring of the intake valve or the exhaust valve.
Thus, in the conventional apparatus described in JP-A-2002-357105 (corresponding to US20020139332), the vane rotor is provided with a lock pin, and the housing is provided with a lock hole. When a projection condition is satisfied, the lock pin is displaced from a retraction position, at which the lock pin is retracted within the vane rotor, to a projection position, at which the lock pin projects from the vane rotor. When the lock pin located at the projection position is fitted into or engaged with the lock hole, the relative rotational phase of the vane rotor is locked such that the vane rotor is prevented from rotating relative to the housing. As a result, if a lock control is executed, in which the relative rotational phase is controlled such that the lock pin is engaged with the lock hole, during the stopping of the engine, the relative rotational phase has been locked accordingly at the start of the engine in the next operation. As a result, it is possible to prevent the wide change of the relative rotational phase at the engine start.
Then, when it becomes possible to supply substantial amount of hydraulic oil after the engine start, and thereby a projection condition becomes unsatisfied, the lock pin is retracted to be received in the vane rotor such that the lock of the relative rotational phase is released. Subsequently, the feed-back control is executed, in which the phase control is controlled based on a difference between the actual phase and the target phase computed in accordance with the engine operational state.
A conventional valve timing adjuster is usually designed such that the phase is locked to a full retard position. However, in a recent apparatus, the phase is alternatively locked to a position between the full retard position and a full advance position, and the inventor of the present invention has found the following disadvantages in the recent apparatus.
In other words, as shown in FIG. 9A, a clearance CL is formed between a side surface (pin side surface 250w) of an advance limitation pin 250 and a wall surface (hole wall surface 211w) of a lock hole 211. However, when the advance limitation pin 250 is displaced from the projection position to the retraction position in a lock release operation, the pin side surface 250w is pressed against the hole wall surface 211w due to an oil pressure difference between the advance chambers and the retard chambers and due to the variable torque (torque reversals), as shown in FIG. 9C and FIG. 9B.
As a result, in a lock mechanism that is configured to lock the phase at a position between the full retard position and the full advance position, because the pin side surface 250w is pressed against the hole wall surface 211w, a frictional force is generated between the pin side surface 250w and the hole wall surface 211w, and thereby the frictional force makes it difficult to disengage the advance limitation pin 250 from the lock hole 211. Thus, it may be impossible to quickly release the lock even when the sufficient hydraulic oil has been supplied after the engine start disadvantageously.
In another lock mechanism that is configured to lock the phase at the full retard position, the above disadvantageous state will not occur when the duration of the state shown in FIG. 9A is elongated by the following setting and operation. The advance limitation pin 250 and the lock hole 211 are designed such that the advance limitation pin 250 is located at the position shown in FIG. 9A when the first rotor and the second rotor are located at the full retard position. Also, the system is controlled such that the oil pressure difference between the advance chamber and the retard chamber is applied in the retard direction. The above setting and operation makes it possible to elongate the duration of the physical relation between the advance limitation pin 250 and the lock hole 211.